Method and apparatus for image forming capable of effectively supporting a recording medium

ABSTRACT

A sheet feeding unit includes a first supporting mechanism configured to support a first area of a recording medium in a range from a leading edge of the recording medium  5  to a first portion extending to an opposite direction to a sheet feeding direction of the recording medium, a second supporting mechanism configured to support a second area of the recording medium in a range from an upstream portion of the first area of the recording medium to a second portion toward a trailing edge of the recording medium, and a third supporting mechanism configured to support a third area of the recording medium in a range from an upstream portion of the second area of the recording medium to a third position after the second portion and toward the trailing edge of the recording medium.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to Japanese patent application no. 2005-118337, filed in the Japan Patent Office on Apr. 15, 2005, the disclosure of which is incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for effectively supporting a long sheet, and more particularly relates to a sheet feeding unit included in an image forming apparatus, the sheet feeding unit for feeding a recording medium having a long length in a sheet feeding direction.

2. Description of the Related Art

It is well known that background image forming apparatuses include a sheet feeding device for feeding a recording medium placed on a sheet feeding tray.

The background image forming apparatuses are electrophotographic copiers, printers, facsimile machines, and multi-functional machines having at least two functions of the electrophotographic copiers, printers, and facsimile machines.

To downsize a background image forming apparatus, the size of a sheet feeding tray attached to the sheet feeding device is required to be formed relatively small.

The sheet feeding tray, however, cannot hold an entire recording medium having a long length in a sheet feeding direction on the sheet feeding tray. For example, the rear portion or trailing edge of the recording medium extends off the sheet feeding tray. If the long sheet is fed with the rear portion or trailing edge off the sheet feeding tray, the long recording medium can be skewed.

To avoid skews of the long recording medium, a technique for a sheet feeding device such that a sheet supporting section supports a long recording medium has been proposed. The sheet supporting section of a sheet feeding tray of the sheet feeding device is provided at a portion below the sheet feeding tray so that a rear portion of the long recording medium staying off the sheet feeding tray is supported by the sheet supporting section. With the sheet feeding device, the long recording medium is fed while guided by the sheet supporting section, which results in a smooth feeding of a recording medium without skewing. The sheet feeding device, however, causes the sheet supporting section, which is provided at the lower part of the sheet feeding tray mounted below lower than the sheet feeding tray, to support the rear portion of the long recording medium that extends off the sheet feeding tray. That is, the above-described structure can cause the long recording medium supported over the sheet feeding tray and the sheet supporting section to fall or slide downwardly by the own weight of the long recording medium.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-described circumstances.

An object of the present invention is to provide a novel sheet feeding unit capable of effectively supporting a recording medium that has a long length in a sheet feeding direction, and to include the novel sheet feeding device in an image forming apparatus.

Another object of the present invention is to provide a method of supporting the recording medium by using the above-described novel sheet feeding unit.

In one embodiment, a novel sheet feeding unit includes a first supporting member configured to support a recording medium thereon, a second supporting member configured to support the recording medium and disposed at an upper portion of the first supporting member, and a third supporting member configured to support the recording medium and disposed at an upper portion of the second supporting member.

The first supporting member may be configured to support a first area of the recording medium in a range from a leading edge of the recording medium to a first portion extending in an opposite direction to a sheet feeding direction of the recording medium.

The second supporting member may be configured to support a second area of the recording medium in a range from an upstream of the first area of the recording medium to a second portion toward a trailing edge of the recording medium and be positioned an upper portion of the first area of the recording medium.

The third supporting member may be configured to support a third area of the recording medium in a range from an upstream of the second area of the recording medium to a third position after the second portion and toward the trailing edge of the recording medium and be positioned at an upper portion of the second area of the recording medium.

The first supporting member may include a sheet feeding tray configured to hold the recording medium, and a pair of side members movably mounted on the sheet feeding tray so that the pair of side members move in a direction perpendicular to the sheet feeding direction.

The second and third supporting members may include a pair of guide members, each of which is detachably attached to a corresponding one of the pair of side members. The pair of guide members may include a first pair of guide portions integrally attached to the pair of respective guide members and included in the second supporting member, and a second pair of guide portions integrally attached to the pair of respective guide members and included in the third supporting member.

Each of the pair of side members may include a lower plate configured to support end portions in a width direction of the first area of the recording medium, a side plate integrally mounted to and substantially vertical with respect to the lower plate and configured to guide a corresponding one of the side ends in a width direction of the recording medium, and an upper plate integrally mounted to the side plate and disposed at an upper portion of the lower plate and configured to detachably be engaged with a corresponding one of the pair of guide members.

The above-described sheet feeding unit may be included in an image forming apparatus.

Further, in one embodiment, a novel method of supporting a recording medium includes supporting a first area of a recording medium in a range from a leading edge of the recording medium to a first portion extending to an opposite direction to a sheet feeding direction of the recording medium, supporting a second area of the recording medium in a range from an upstream portion of the first area of the recording medium to a second portion toward a trailing edge of the recording medium, and supporting a third area of the recording medium in a range from an upstream portion of the second area of the recording medium to a third position after the second portion and toward the trailing edge of the recording medium.

The supporting of the first area may include holding a lower surface of the recording medium, and leading the recording medium while holding the recording medium.

The supporting of the second and third areas may include guiding the recording medium with first and second pairs of guide portions.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

FIG. 1 is a cross sectional view of the schematic structure of an image forming apparatus including a manual sheet feeding unit according to an exemplary embodiment of the present invention;

FIG. 2 is a perspective view showing the detailed structure of the manual sheet feeding unit of FIG. 1;

FIG. 3 is a partly cross sectional view of the manual sheet feeding unit of FIG. 2; and

FIG. 4 is a perspective view of the manual sheet schematic detailed feeding unit of FIG. 2 when guide members of the manual sheet feeding unit are detached from side fences mounted on the manual sheet feeding unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In describing preferred embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner.

Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, preferred embodiments of the present invention are described.

Referring to FIG. 1, a schematic structure of an image forming apparatus 100 including a manual sheet feeding unit 16 according to an exemplary embodiment of the present invention is described.

In FIG. 1, a main body 10 of the image forming apparatus 100 includes drum-shaped four photoconductive elements ly, 1 c, 1 m, and 1 bk, an intermediate transfer belt 2, an optical writing unit 6, a fixing unit 13, and a main sheet feeding unit 7.

The photoconductive elements 1 y, 1 c, 1 m, and 1 bk serve as an image forming mechanism. The photoconductive elements 1 y, 1 c, 1 m, and 1 bk can have similar structures and functions, except that the toners are different colors to form yellow images, cyan images, magenta images, and black images, respectively.

The photoconductive elements 1 y, 1 c, 1 m, and 1 bk separately receive respective light laser beams emitted by the optical writing unit 6, such that electrostatic latent images are formed on the surfaces of the four photoconductive elements 1 y, 1 c, 1 m, and 1 bk.

Respective charging rollers (not shown) are held in contact with the photoconductive elements 1 y, 1 c, 1 m, and 1 bk to charge respective surfaces of the photoconductive elements 1 y, 1 c, 1 m, and 1 bk.

The optical writing unit 6 serves as a writing mechanism. The optical writing unit 6 is provided at a position below the photoconductive elements 1 y, 1 c, 1 m, and 1 bk. As previously described, the writing unit 6 emits the respective light laser beams to respective surfaces of the photoconductive elements 1 y, 1 c, 1 m, and 1 bk to form the respective electrostatic latent images thereon.

Respective developing units (not shown) are separately disposed in a vicinity of or adjacent to the photoconductive elements 1 y, 1 c, 1 m, and 1 bk, respectively. The respective developing units store the different colored toners for the photoconductive elements 1 y, 1 c, 1 m, and 1 bk.

The intermediate transfer belt 2 serves as a transfer mechanism, and is located or disposed above the photoconductive elements 1 y, 1 c, 1 m, and 1 bk. The intermediate transfer belt 2 forms an endless belt and is passed over or surrounds a plurality of supporting rollers 3, 4, and 5. The intermediate transfer belt 2 is held in contact with the photoconductive elements 1 y, 1 c, 1 m, and 1 bk, and is driven to rotate clockwise as indicated by arrow A as shown in FIG. 1.

In FIG. 1, an intermediate transfer belt cleaning unit 15 is provided in the left side of the supporting roller 4. The intermediate transfer belt cleaning unit 15 removes a residual toner on the intermediate transfer belt 2 after image formation.

Four primary transfer unit 50 y, 50 c, 50 m, and 50 bk are disposed inside a loop of the intermediate transfer belt 2 to face the respective photoconductive elements 1 y, 1 c, 1 m, and 1 bk.

A secondary transfer roller 12 is located on the opposite side of the supporting roller 3, sandwiching the intermediate transfer belt 2.

The fixing unit 13 is positioned at a upper right side of the main body 10, in a vicinity of the secondary transfer roller 12 and the supporting roller 3. The fixing unit serves as a fixing mechanism, and includes a fixing belt (not shown) and a pressure roller (not shown).

The main sheet feeding unit 7 serves as a sheet feeding mechanism, and is located at a lower part of the main body 10 of the image forming apparatus 100. The main sheet feeding unit 7 includes a sheet feeding cassette 8. The sheet feeding cassette 8 is loaded with a stack of sheets of particular size, including a main recording sheet MS. When an image forming operation is performed, the main recording sheet MS is fed by a sheet feeding roller 9 with predetermined timing from the sheet feeding cassette 8 and is conveyed in a direction indicated by arrow B in FIG. 1 toward a pair of registration rollers 11.

The manual sheet feeding unit 16 is rotatably mounted on the right side of the main body 10 of the image forming apparatus 100 of FIG. 1, and includes a sheet feeding tray 17, a manual sheet feeding roller 18, a pair of side fences 19 including side fences 19 a and 19 b (see FIG. 2), and a guide member 20 including guide members 20 a and 20 b (see FIG. 2). An operator of the image forming apparatus 100 can feed sheets by hand using the manual sheet feeding unit 16.

Operations of the above-described image forming apparatus 100 are now described.

When the image forming apparatus 100 receives image data, each of the photoconductive elements 1 y, 1 c, 1 m, and 1 bk rotates in a clockwise direction in FIG. 1 and are uniformly charged with the corresponding charging rollers (not shown). The writing unit 6 emits the light laser beams corresponding to the respective image data, and irradiates the photoconductive elements 1 y, 1 c, 1 m, and 1 bk. Electrostatic latent images corresponding to the respective image data are formed on the respective surfaces of the photoconductive elements 1 y, 1 c, 1 m, and 1 bk. The electrostatic latent images formed on the respective photoconductive elements 1 y, 1 c, 1 m, and 1 bk are visualized by the respective developing units (not shown), which contain respective color toners therein, into yellow, cyan, magenta, and black toner images, respectively. Those color toner images are sequentially overlaid on the surface of the intermediate transfer belt 2 such that a composite color image is formed on the surface of the intermediate transfer belt 2.

When the image forming operation is started, the sheet feeding roller 9 starts to rotate so that the main recording sheet MS is conveyed toward the pair of registration rollers 11 in the direction indicated by the arrow B. When manual insertion is used, the manual sheet feeding roller 18 is rotated to feed a recording sheet placed on the manual sheet feeding tray 17, and transfers the recording sheet via a pair of sheet conveying rollers 40 to the pair of registration rollers 49.

Then, the pair of registration rollers 11 stops and feeds the main recording sheet MS in synchronization with a movement of the composite color image towards a transfer area formed between the intermediate transfer belt 2 and the secondary transfer roller 12.

The main recording sheet MS that has the composite color image thereon is further conveyed and passes through the fixing unit 13. The fixing unit 13 fixes the composite color image to the main recording sheet MS by applying heat and pressure.

After the main recording sheet MS passes through the fixing unit 13, the main recording sheet MS is discharged to a sheet discharging tray 14.

After the composite color image is transferred onto the main recording sheet MS, the intermediate transfer belt cleaning unit 15 removes residual toner on the surface of the intermediate transfer belt 2 before a next image forming operation is ready to start.

Referring to FIGS. 2, 3, and 4, the detailed structures of the manual sheet feeding unit 16 according to the present invention are described.

In FIG. 2, the manual sheet feeding unit 16 includes the sheet feeding tray 17, the sheet feeding roller 18, the pair of side fences 19 a and 19 b or the side fences 19 a and 19 b, and the pair of guide members 20 a and 20 b or the guide members 20 a and 20 b. As shown in FIGS. 2 and 3, the pair of guide members 20 a and 20 b are detachably attached to the pair of side fences 19 a and 19 b, respectively. In FIG. 2, a portion of a recording sheet S to be inserted into the main body 10 of the image forming apparatus 100 is identified by an alternate long and two short dashes line. FIG. 3 shows the recording sheet S by a solid line. FIG. 4 shows the manual sheet feeding unit 16 in which the guide members 20 a and 20 b are detached from the side fences 19 a and 19 b, respectively. The recording sheet S is conveyed in a direction indicated by arrow C in FIGS. 2, 3, and 4. The sheet feeding roller 18 is fixedly supported by the rotating shaft 21. The rotating shaft 21 includes both ends in a longitudinal direction, and the both ends are rotatably supported by the sheet feeding tray 17.

As shown in FIG. 4, the side fences 19 a and 19 b are movably mounted on the sheet feeding tray 17 such that the side fences 19 a and 19 b can move in a direction perpendicular to the direction indicated by arrow C to which the recording sheet S is conveyed. As is conventionally well known, it is preferable that when an operator manually moves one of the side fences 19 a and 19 b in a width direction of the recording sheet S, toward the other of the side fences 19 a and 19 b, the other of the side fences 19 a and 19 b automatically moves close to the one of the side fence 19 a or 19 b by the same distance the one of side fences 19 a and 19 b moves. More specifically, when an operator moves the side fence 19 a in a direction toward the side fence 19 b, the side fence 19 b automatically moves in a direction toward the side fence 19 a. It is also preferable that the identical operation be performed when the operator manually moves the other of the side fences 19 a and 19 b in the width direction of the recording sheet S, toward the one of the side fences 19 a and 19 b. More specifically, when an operator moves the side fence 19 b in a direction toward the side fence 19 a, the side fence 19 a automatically moves in a direction toward the side fence 19 b.

As shown in FIG. 4, the side fences 19 a and 19 b are disposed facing each other, and are formed in a symmetric manner. The side fences 19 a and 19 b include respective lower plates 22 a and 22 b, respective side plates 23 a and 23 b, respective upper plates 24 a and 24 b. The lower plates 22 a and 22 b are slidably mounted on the sheet feeding tray 17. The side plates 23 a and 23 b are mounted substantially vertical with respect to the lower plates 22 a and 22 b, respectively. The upper plates 24 a and 24 b are mounted at a portion above the lower plates 22 a and 22 b, respectively. The lower plate 22 a, the side plate 23 a, and the upper plate 24 a of the side fence 19 a are integrally mounted, and the lower plate 22 b, the side plate 23 b, and the upper plate 24 b of the side fence 19 b are integrally mounted.

When each of the side fences 19 a and 19 b is moved in a direction perpendicular to the direction indicated by arrow C to which the recording sheet S is conveyed, each of the side fences 19 a and 19 b can be moved in the width direction of the recording sheet S, and each of the lower plates 22 a and 22 b of the respective side fences 19 a and 19 b can be slidably moved on the sheet feeding tray 17.

As shown in FIGS. 2 and 3, the recording sheet S that has a long length in a sheet feeding direction is placed on the sheet feeding unit 16. At this time, as shown in FIG. 3, the range from a leading edge 32 of the recording sheet S to a first portion extending to an opposite direction to the sheet feeding direction, indicated by arrow C, of the recording sheet S is defined as a first area of sheet S1. The first area of sheet S1 is supported by the lower plate 22 a of the side fence 19 a and the lower plate 22 b of the side fence 19 b. That is, as shown in FIG. 2, the side fences 19 a and 19 b are moved in the width direction of the recording sheet S so that both side ends 33 a and 33 b of the recording sheet S are lightly held in contact with the side plates 23 a and 23 b of the side fences 19 a and 19 b, respectively. More specifically, the side end 33 a of the recording sheet S can be supportably held in contact with the side plate 23 a of the side fence 19 a, and the side end 33 b of the recording sheet S can be supportably held in contact with the side plate 23 b of the side fence 19 b. With the above-described structure, end portions 34 a and 34 b in the width direction of the recording sheet S can be placed on the lower plates 22 a and 22 b of the side fences 19 a and 19 b, respectively, and the rest portion of the recording sheet S can be placed on the sheet feeding tray 17.

As described above, the manual sheet feeding unit 16 of this embodiment includes the sheet feeding tray 17 and the pair of side fences 19 a and 19 b that are movably mounted on the sheet feeding tray 17 such that the side fences 19 a and 19 b can move in the direction perpendicular to the direction indicated by arrow C to which the recording sheet S is conveyed. The sheet feeding tray 17 and the pair of side fences 19 a and 19 b form a first supporting portion 17 s to support the first area of sheet S1 having the range from the leading edge 32 of the recording sheet S to the first portion extending to the opposite direction to the sheet-feeding direction C of the recording sheet S. In addition, the side fences 19 a and 19 b respectively include the lower plates 22 a and 22 b to support the end portions 34 a and 34 b in the width direction of the first area of sheet S1 of the recording sheet S. The first supporting portion 17 s serves as a first supporting mechanism.

Similar to the side fences 19 a and 19 b, the guide members 20 a and 20 b are disposed facing each other, and are formed in a symmetric manner.

As shown in FIGS. 2 and 3, the guide members 20 a and 20 b respectively include second supporting portions 26 a and 26 b, and third supporting portions 28 a and 28 b. The second supporting portions 26 a and 26 b serve as a second supporting mechanism, and include lower guides 25 a and 25 b serving as a pair of guide portions, respectively. The third supporting portions 28 a and 28 b serve as a third supporting mechanism, and include upper guides 27 a and 27 b serving another pair of guide portions, respectively, which are disposed at respective upper portions of the lower guides 25 a and 25 b. The lower and upper guides 25 a and 27 a are mounted on lower and upper portions, respectively, of the guide member 20 a are integrally attached via a side guide 29 a, and the lower and upper guides 25 b and 27 b are also mounted on lower and upper portions, respectively, of the guide member 20 b are integrally attached via a side guide 29 b.

As shown in FIG. 3, the lower guide 25 a provided at the lower portion of the guide member 20 a includes a plurality of engaging pawls 30 a. The plurality of engaging pawls 30 a can be mounted in a protruding manner on the lower surface of the lower guide 25 a. The plurality of engaging pawls 30 a can be detachably engaged with a plurality of engaging holes 31 a (shown in FIG. 4) that are formed on the upper surface of the upper plate 24 a of the side fence 19 a. With the above-described structure, the guide member 20 a can be detachably mounted on the side fence 19 a.

As same as described above, the guide member 20 b can be detachably mounted on the side fence 19 b by engaging a plurality of engaging pawls (not shown) mounted in a protruding manner on the lower surface of the lower guide 25 b of the guide member 20 b with a plurality of engaging holes pawls 30 a can detachably 31 b (shown in FIG. 4) that are formed on the upper surface of the upper plate 24 b of the side fence 19 b. Thus, the guide members 20 a and 20 b are detachably mounted on and engaged with the upper plates 24 a and 24 b of the side fences 19 a and 19 b, respectively.

The first area of sheet S1 of the recording sheet S placed on the sheet feeding unit 16 is supported by the first supporting portion 17 s as described above.

As shown in FIGS. 2 and 3, a range of the recording sheet S from an upstream of the first area of sheet S1 to a second portion toward the trailing edge 35 of the recording sheet S, which is positioned at an upper portion of the first area of sheet S1, is defined as a second area of sheet S2. The second area of sheet S2 is supported by the second supporting portions 26 a and 26 b of the respective guide members 20 a and 20 b. Both side ends 33 a and 33 b of the second area of sheet S2 are lightly held in contact with the side guide plate 29 a and 29 b of the respective guide members 20 a and 20 b, respectively. More specifically, the side end 33 a of the recording sheet S in the second area of sheet S2 can be supportably held in contact with the side guide plate 29 a of the guide member 20 a, and the side end 33 b of the recording sheet S in the second area of sheet S2 can be supportably held in contact with the side guide plate 29 b of the guide member 20 b.

Another range of the recording sheet S from an upstream of the second area of sheet S2 to a third portion after the second portion and toward the trailing edge 35 of the recording sheet S, which is positioned at an upper portion of the second area of sheet S2, is defined as a third area of sheet S3. The third area of sheet S3 is supported by the third supporting portions 28 a and 28 b of the respective guide members 20 a and 20 b. Both side ends 33 a and 33 b of the third area of sheet S3 are lightly held in contact with upper side guide plates 36 a and 36 b that are formed at respective upper portions of the side guide plates 29 a and 29 b of the respective guide members 20 a and 20 b, respectively. More specifically, the side end 33 a of the recording sheet S in the third area of sheet S3 can be supportably held in contact with the upper side guide plate 36 a of the guide member 20 a, and the side end 33 b of the recording sheet S in the third area of sheet S3 can be supportably held in contact with the upper side guide plate 36 b of the guide member 20 b.

As described above, the manual sheet feeding unit 16 according to the present invention includes the first supporting portion 17 s to support the first area of sheet S1, the second supporting portions 26 a and 26 b to support the second area of sheet S2, and the third supporting portions 28 a and 28 b to support the third area of sheet S3. The second and third supporting portions 26 a and 28 a are formed on the guide member 20 a that is detachably mounted on the side fence 19 a, and the second and third supporting portions be held in contact be held in contact with the 26 b and 28 b are formed on the guide member 20 b that is detachably mounted on the side fence 19 b.

With the above-described structures, the recording sheet S placed on the manual sheet feeding unit 16 are positioned so that the first, second, and third portions of sheet S1, S2, and S3 are sequentially folded up from a lower portion to an upper portion of the guide members 20 a and 20 b detachably mounted on the side fences 19 a and 19 b, respectively, of the manual sheet feeding unit 16. Thus, the recording sheet S having a long length in the sheet feeding direction can be stably placed, and the trailing edge 35 of the recording sheet S may not slide and fall from the sheet feeding tray 17 of the manual sheet feeding unit 16.

Here, when an operator presses a print key (not shown), the sheet feeding roller 18 is driven to rotate in a direction indicated by arrow D as shown in FIGS. 2 and 3. With the above-described operation, the recording sheet S is fed to the direction indicted by arrow C, and thereafter, is conveyed inside the image forming apparatus 100. At this time, the recording sheet S having a long length in the sheet feeding direction can be guided by the first, second, and third supporting portions of the sheet feeding unit 16. Therefore, the recording sheet S can be fed into the image forming apparatus 100 without becoming skewed. Further, the side ends 33 a and 33 b in the width direction of the recording sheet S are guided or led by the side plates 23 a and 23 b of the respective side fences 19 a and 19 b and the side guide plates 29 a and 29 b and the upper side guide plates 36 a and 36 b of the respective guide members 20 a and 20 b. Therefore, the recording sheet S can be more assuredly prevented from becoming skewed.

The sheet feeding tray 17 is supported in an openable and rotatable manner with respect to the main body 10 of the image forming apparatus 100. When the manual sheet feeding unit 16 is not used, the sheet feeding tray 17 can be stored as indicated by the long and two short dashes line in FIG. 1. The image forming apparatus 100 in FIG. 1 has a room to rotatably fold the sheet feeding tray 17 to its closed position with the guide members 20 a and 20 b being detached from the respective side fences 19 a and 19 b so that the sheet feeding tray 17 and the side fences 19 a and 19 b are rotatably moved to the closed position to store. As described in the embodiment, however, the sheet feeding tray 17 can be stored with the guide members 20 a and 20 b being constantly attached to the respective side fences 19 a and 19 b.

The guide members 20 a and 20 b of the manual sheet feeding unit 16 include the second and third supporting portions 26 a, 26 b, 28 a, and 28 b, respectively. However, as an alternative, the present invention can provide at least one additional supporting portion at a position above the third supporting portion 28 a and 28 b so that the at least one additional supporting portion can support the trailing edge of the recording sheet S.

The present invention can be applied to a sheet feeding unit other than the manual sheet feeding unit, for example, an automatic document feeder (ADF). Further, the present invention can be applied to a sheet feeding unit included in another image forming apparatus, for example, a copier, printer, facsimile machine, and a multi-functional machine including functions of the copier, printer, and facsimile machine. Furthermore, the present invention can be applied to a sheet feeding unit included in an image scanner.

The above-described embodiments are illustrative, and numerous additional modifications and variations are possible in light of the above teachings. For example, elements and/or features of different illustrative and exemplary embodiments herein may be combined with each other and/or substituted for each other within the scope of this disclosure and appended claims. It is therefore to be understood that within the scope of the appended claims, the disclosure of this patent specification may be practiced otherwise than as specifically described herein. 

1. A sheet feeding unit, comprising: a first supporting mechanism configured to support a recording medium on thereon; a second supporting mechanism configured to support the recording medium, and which is disposed at an upper portion of the first supporting mechanism; and a third supporting mechanism configured to support the recording medium, and which is disposed at an upper portion of the second supporting mechanism.
 2. The sheet feeding unit according to claim 1, wherein: the first supporting mechanism is configured to support a first area of the recording medium in a range from a leading edge of the recording medium to a first portion extending to an opposite direction to a sheet feeding direction of the recording medium; the second supporting mechanism is configured to support a second area of the recording medium in a range from an upstream of the first area of the recording medium to a second portion toward a trailing edge of the recording medium and be positioned an upper portion of the first area of the recording medium; and the third supporting mechanism is configured to support a third area of the recording medium in a range from an upstream of the second area of the recording medium to a third position after the second portion and toward the trailing edge of the recording medium and be positioned at an upper portion of the second area of the recording medium.
 3. The sheet feeding unit according to claim 2, wherein: the first supporting mechanism comprises: a sheet feeding tray configured to hold the recording medium; and a pair of side members movably mounted on the sheet feeding tray so that the pair of side members are movable in a direction perpendicular to the sheet feeding direction, the second and third supporting mechanisms comprise a pair of guide members, each of which is detachably attached to a corresponding one of the pair of side members, the pair of guide members comprising: a first pair of guide portions, each of which is integrally attached to a corresponding one of the pair of guide members, and is included in the second supporting mechanism; and a second pair of guide portions, each of which integrally attached to a corresponding one of the pair of guide members, and is included in the third supporting mechanism.
 4. The sheet feeding unit according to claim 3, wherein: the pair of side members, each of which comprises: a lower plate configured to support end portions in a width direction of the first area of the recording medium; a side plate integrally mounted substantially vertical with respect to the lower plate, and configured to guide a corresponding one of side ends in a width direction of the recording medium; and an upper plate integrally mounted to the side plate and disposed at an upper portion of the lower plate, and configured to detachably be engaged with a corresponding one of the pair of guide members.
 5. The sheet feeding unit according to claim 1, wherein the sheet feeding unit is included in an image forming apparatus.
 6. A sheet feeding unit, comprising: first means for supporting a first area of a recording medium in a range from a leading edge of the recording medium to a first portion extending to an opposite direction to a sheet feeding direction of the recording medium; second means for supporting a second area of the recording medium in a range from an upstream portion of the first area of the recording medium to a second portion toward a trailing edge of the recording medium; and third means for supporting a third area of the recording medium in a range from an upstream portion of the second area of the recording medium to a third position after the second portion and toward the trailing edge of the recording medium.
 7. The sheet feeding unit according to claim 6, wherein: the first means for supporting comprises: means for holding a lower surface of the recording medium; and means for leading the recording medium with the means for holding, wherein said second and third means for supporting comprise means for guiding the recording medium including: a first pair of guide portions integrally attached to the means for leading and included in the second means for supporting; and a second pair of guide portions integrally attached to the means for leading and included in the third means for supporting.
 8. The sheet feeding unit according to claim 6, wherein: the first, second, and means for supporting are included in an image forming apparatus.
 9. A method of feeding of supporting a recording medium, comprising: supporting a first area of a recording medium in a range from a leading edge of the recording medium to a first portion extending to an opposite direction to a sheet feeding direction of the recording medium; supporting a second area of the recording medium in a range from an upstream portion of the first area of the recording medium to a second portion toward a trailing edge of the recording medium; and supporting a third area of the recording medium in a range from an upstream portion of the second area of the recording medium to a third position after the second portion and toward the trailing edge of the recording medium.
 10. The method according to claim 9, wherein: the supporting of the first area comprises: holding a lower surface of the recording medium; and leading the recording medium while holding the recording medium, and the supporting of the second and third areas comprises guiding the recording medium with first and second pairs of guide portions. 